1. Field of the Invention
The present invention relates to devices provided with an electrostatic sensor as an input apparatus.
2. Description of the Related Art
A remote control apparatus (referred to below as “remote controller”) is used for remote control of target objects that are located at a distance from a user, such as a television set, an audio device, or an air conditioner. In recent years there has been progress to the extent of using a remote control key for locking and unlocking an automobile, and even for starting an engine.
In general a remote controller is provided with an operating part including a button or switch that receives a user's instruction input, and a transmitter that encodes the instruction input which has been inputted through the operating part, and modulates a light beam, an infra-red ray, or a radio wave, to be transmitted to the target object. Conventional operating parts have generally monitored contact and non-contact of electrodes by a mechanical switch.
However, with the mechanical switch there is a problem in that wear occurs due to repeated pressing. Also, when the mechanical switch is installed in a remote controller, there has been a problem of water resistance due to a gap occurring between a moving part of the switch, that is, the button, and a casing. This problem is particularly significant for an automobile remote control key that is used outdoors.
In recent years, instead of the mechanical switch an electrostatic sensor has begun to be used. The electrostatic sensor is a device in which the distance between two electrodes that are arranged opposite each other is changed by the electrodes being pressed, and change of electrostatic capacitance is used to detect and analyze input from the user. For example, Patent Document 1 discloses an input device that uses this change of electrostatic capacitance of an electrode pair.
The electrostatic sensor has excellent durability in comparison to the mechanical switch, and since it can be installed inside a hermetically sealed casing, it is also excellent from the point of view of water resistance. Consequently, there have been various efforts to install the electrostatic sensor in remote controllers and electronic devices.
Patent Document 1: Japanese Patent Application, Laid Open No. 2001-325858
Patent Document 2: Japanese Patent Application, Laid Open No. 2000-308159
Patent Document 3: Japanese Patent Application, Laid Open No. 2007-104204
Patent Document 4: Japanese Patent Application, Laid Open No. H10-59131
The electrostatic sensor performs detection by converting electrostatic capacitance to voltage. Therefore, since there is a need to constantly monitor the electrostatic capacitance in order to judge a state of operation input by the user, it is necessary to constantly operate a circuit that converts the electrostatic capacitance to an electrical signal, and there is a problem in that power consumption increases in comparison to the mechanical switch. Furthermore, taking an automobile remote controller as an example, if a switch that is in a pocket or a bag is unintentionally pressed, a target object will be operated by mistake.
This type of problem is not limited to remote controllers, and may occur in various types of electronic device in which an operating part of an electrostatic sensor is provided on a surface of the casing.